Apparatus for stacking hides or the like

ABSTRACT

This apparatus is adapted to stack hides or the like of different lengths successively and centrally on each other so as to straddle the narrow head of an upwardly tapering hide support so that the two halves of each hide will be disposed at the front and rear sides of this support and the superimposed hides form a centrally folded stack which takes up very little space and is so accurately balanced on the head of the support that it will not tip over. The apparatus comprises a pair of conveyor belts behind each other, a scanning device, preferably a photoelectric cell, for measuring the length of each hide while traveling along the first conveyor belt and for thereby also determining the position of the center of each hide, and a control mechanism which is responsive to the actuation of the scanning device and controls the operation of the second conveyor belt which receives at least a part of the hide form the first belt and then moves the hide toward the hide support and deposits the hide centrally in the straddling position on the support or on the previously deposited hide.

1 snow? 0 M A Unit States l [72] Inventor Cornelius Van Durst Rijen, Netherlands 121] App]. No. 5,857 {22] Filed Jan. 26, 1970 [45] Patented Sept. 7, 11971 [73] Assignee Badiscbe Maschinenlinbrilk G.m.b.llil. [32] Priority Jan. 27, W69 [33] Nether 31 1 s 901 282 l [54] APPARATUS FOR STACKHNG lHllLIDES OR THE lLlMIE 14 Claims, 4 Drawing Figs.

[52] U5. Cl 271/65, 271/68 [51] llnt. lCl lB6h 295d [50] Field of ch 271/65, 68, 86. 63

[56] References Cited UNITED STATES PATENTS 3,156,464 ll/l964 Piskytl etal. 27l/86X 3,198,513 8/l965 Farez AMSTIRACT: This apparatus is adapted to stack hides or the like of different lengths successively and centrally on each other so as to straddle the narrow head of an upwardly tapering hide support so that the two halves of each hide will be disposed at the front and rear sides of this support and the superimposed hides form a centrally folded stack which takes up very little space and is so accurately balanced on the head of the support that it will not tip over. The apparatus comprises a pair of conveyor belts behind each other, a scanning device, preferably a photoelectric cell, for measuring the length of each hide while traveling along the first conveyor belt and for thereby also determining the position of the center of each hide, and a control mechanism which is responsive to the actuation of the scanning device and controls the operation of the second conveyor belt which receives at least a part of the hide form the first belt and then moves the hide toward the hide support and deposits the hide centrally in the straddling position on the support or on the previously deposited hide.

PATENIEnsEP 7m 3.603, 587 SHEET 2 or 3 INVEN TOR conusprus vnoonsr w mjawv APPARATUS FQR STAClKllN G lllllllDES OR THE lLlKlE The present invention relates to an apparatus for stacking hides, skins or the like on each other in a straddling position on a narrow support such as a trestle or the like.

Such apparatus are employed in the leather processing and leather goods industry for doing the work which previously had to be carried out by manual labor. Various kinds of apparatus have already been developed for carrying out such stacking operations mechanically. In all of these apparatus the problem had to be solved that the hides to be stacked differ very much in shape and especially in length from each other. If these hides which often have a considerable weight were stacked haphazardly on each other in a straddling position on a narrow support, the stack would easily tip over and collapse since the center of gravity of the stack would usually be located at one or the other side of the projecting head ofthe support. Special precautions must therefore always be taken when employing such stacking apparatus so that the individual hides will be placed centrally upon each other.

Another difficulty which frequently occurs when stacking hides is due to the fact that it is often desired to deposit each pair of superimposed hides of a stack so that their flesh sides face each other since the individual hides will then remain moist more uniformly.

One prior stacking apparatus as disclosed by the German Pat. No. 1,220,789 tends to solve these difficulties and comprises a conveyor belt which travels in one direction for feeding the hides successively to the support on which they are to be stacked, Above this conveyor belt a series of light sources are provided for producing two large lighted areas or light fields behind each other. Each hide is then passed successively through these two light fields and the light penetrating through and diminished by the hide is measured. When the light penetrating through the hide in both light fields has the same intensity, the center of gravity of the hide is located centrally between the two light fields. The other elements of the stacking apparatus are then controlled in dependence upon the point of time when this measurement is carried out. The most important of these elements is another conveyor belt which travels in the direction opposite to the first conveyor and is movable back and forth as a unit over the hide support relative to the first belt unit which is mounted in a fixed positron.

The delivery end of the first conveyor belt extends over the hide support so that when the hide passes beyond this end, its front edge hangs down at the rear side of the support. At a certain point of time which is determined by the light-scanning device, the second conveyor belt is moved as a unit against the downwardly suspended part of the hide and shifts the same toward the support and deposits the hide thereon in such a manner that approximately the center of the length of thehide will be disposed on the narrow projecting head ofthe support. The shifting movement of the second conveyor unit is then interrupted until a further hide is received by the second conveyor belt and is moved by the latter up to the delivery end of this belt so that the front edge of this hide is suspended at the front side of the hide support as seen from the first conveyor. At this movement, the second conveyor unit starts to move back from the first conveyor unit so that the hide is deposited on the support in an upside-down position to the previous hide. The second conveyor unit is then moved back to its original position before it again carries out its first operation by depositing the next hide coming from the first conveyor belt upon the previous hide on the hide support.

The apparatus as above described has the disadvantage that there is a series of dead times in the function of its elements which are due to the particular construction of this apparatus and especially its control mechanism and considerably reduce the efficiency of this apparatus. Furthermore, the control mechanism of this apparatus consists of a large number of elements and a relatively complicated electric circuit which render the apparatus very expensive. This is also due to the fact that the costs of production of the photoelectric scanning device of this apparatus which requires large light fields are very high.

It is an object of the present invention to provide a stacking apparatus which is a simpler construction, may be produced at a lower cost and operates more economically than the apparatus as previously described. Another object of the invention is to design this apparatus in a manner so as to permit the hides to be stacked on each other so that either the same side of all hides will face upwardly or downwardly or that the same sides, for example, the flesh sides, of each pair of the superimposed hides will face each other.

For attaining these objects, the present invention provides an apparatus which essentially consists of two conveyor belts longitudinally behind each other, a simple scanning device or the like, a control mechanism for controlling the operation of one of the belts, and a hide support which may, for example, be tapering upwardly so as to end in a narrow head which is located underneath the adjacent ends of the two conveyor belts. The first conveyor belt which runs at a constant speed in of the first belt to the second belt which at first travels in the same direction and takes up at least a part of thehide and then reverses its direction of travel so as to move the hide or hide part toward the hide support and to deposit the hide'in a straddlingposition on the narrow head of the support. The control mechanism is responsive to the actuation of the scanning device and controls the movements of the second conveyor belt in such a manner thatthe individual hides regardless of their different lengths will be deposited centrally on the head of the hide support and on each other. The two halves of each hide will then be disposed at the front and rear sides of the hide-support and the superimposed hides will form a centrally folded stack which takes up very little space.

important features of the invention further consist in mounting the first conveyor unit in a fixed position in which the front or delivery end of its belt which travels at a constant speed toward this end is located above the head of the hide support but is spaced longitudinally from the central vertical plane of this support, and in providing means for moving the second conveyor unit from a first position to a second position and vice versa. 'ln the first position, the rear end of the second conveyor unit is located underneath the front end of the first conveyor belt but also above the level of the head of the hide support. The belt of this second unit then travels in the same direction as the first belt until it arrives in its second position in which the rear end of this second unit is spaced at a certain distance longitudinally from its first position. This movement of the second conveyor unit is started by the control mechanism of the apparatus during the transfer of the hide from the first conveyor belt to the second conveyor belt and it is stopped at the moment in which the center of the hide which has been determined by the scanning device is located between the delivery end of the first belt and the rear end of the second conveyor unit and vertically above the center of the head of the hide support. As soon as the second conveyor unit is stopped in this position, the: movement of its belt is reversed so that this belt now travels in the direction toward the first conveyor unit.

The length of the hide is therefore at first measured by the scanning device while traveling along the first conveyor belt and the hide is then partly transmitted to the second conveyor belt, Assoon as the center of the hide which has been determined by the scanning device and recorded .by the control mechanism is located vertically above the head of the hide support, the second conveyor unit is moved for a certain distance forwardly and away from the delivery end of the first conveyor belt so that between the two belts the hide is unsupported above the head of the support. Since the belt of the second conveyor unit reverses its direction of travel as soon as this unit is stopped at its forward end position remote from the first conveyor unit, both belts will then run toward each other with the result that the central part of the hide drops downwardly between the two belts, its center falls upon the narrow head of the hide support, and the two halves of the hide fall upon the front and rear sides of the support. When the apparatus operates in the manner as previously described, all hides will be deposited centrally with the same side on the hide support and on each other. During the stacking operation practically no dead times will occur since the second conveyor unit may be moved back at a high speed from its forward end position to its original position in which it receives a part of the next hide from the first conveyor belt. The speed of this return movement of the second conveyor unit toward the first unit is determined by the distance between two successive hides on the first conveyor belt.

In order to stack the hides on each other so that every other hide coming from the first conveyor belt will be reversed so that, for example, the flesh sides of each pair of superimposed hides will face each other and will therefore better retain their uniform moisture content within the stack, the present invention further provides that, after one hide has been conveyed and deposited in the manner as previously described and the second conveyor unit has been returned to its original position, the control mechanism will not start the movement of the second conveyor unit to its forward end position and then reverse the direction of travel of its belt until the next hide coming from the first conveyor belt has been completely transferred to the second conveyor belt. The second conveyor belt then moves the hide back in the direction toward the first conveyor unit and downwardly over the rear end of the second unit until slightly more than one half of the length of this hide including its center hangs down over the rear end of this second unit and the rear edge of this hide hangs over the rear side of the hide support. When the hide arrives in this position on the rearwardly traveling second conveyor belt, the control mechanism starts the return movement of the second conveyor unit to its original position in which its rear end is again located approximately underneath the front end of the first conveyor unit and above and slightly behind the vertical center of the head of the hide support. Since during this return movement of the second conveyor unit its belt travels in the same direction, it rolls the second half of the hide over the head of the hide support to the front side thereof. The center of this hide will then be in engagement with the center or apex of the head of the hide support, but the side of the hide which was facing upwardly while traveling on the conveyor belts will now face downwardly.

Although the mode of operation of the apparatus as last described may also be applied for depositing all hides successively on the hide Support by reversing them relative to the position in which they are located on the conveyor belts, the mode of operation as first described is more preferable if the same side of all hides of a stack should face in the same direction. The second mode of operation is primarily intended for being employed in combination with the first mode so that the hides are alternately disposed face up and face down in the stack. This may be effected by means of the control mechanism.

According to one preferred embodiment of the invention, both conveyor belts are driven by a belt or chain drive so as to run at the identical speed in the same direction or in opposite directions to each other. If this drive comprises a single drivebelt or chain which constantly drives the first conveyor belt in one direction, the second conveyor belt may be driven alternately in the same direction or in the opposite direction by alternately connecting its drive wheel or pulley to one side or to the opposite side of the drivebelt or chain.

This may be effected, for example, by mounting three pulleys in a triangular formation. One of these pulleys also forms the drive pulley of the first conveyor belt while either of the pulleys may be driven by a motor. The belt may then run from the first pulley, for example, the drive pulley of the first conveyor belt, to the second pulley and back to and over the first pulley and again to and over the second pulley and then to the third pulley from which it returns to the first pulley. The drive pulley for the second conveyor belt may then be disposed, for example, at all times at the inside of the triangular arrangement and be shifted into driving engagement with the outer side of the part of the drivebelt running back from the second to the first pulley and will then drive the second conveyor belt in one direction, or this drive pulley may be shifted away from this position and into driving engagement, for example, with the inner side of the part of the belt running from the third pulley to the first pulley and will then drive the second belt in the opposite direction.

For shifting the second conveyor unit from one end position, in which its drive pulley is in driving engagement with one side of the drivebelt, to its other end position in which its drive pulley is in driving engagement with the other side of the drivebelt, this conveyor unit is preferably movable in a guideway which also limits these two end positions. in one of these end positions, the rear end of the second conveyor unit is located underneath the front or delivery end of the first conveyor unit and the conveyor belt of this second unit then receives the hide from the conveyor belt of the first unit, while in the other end position of the second conveyor unit in which it is moved forwardly and away from the first unit, its rear end is disposed at substantially the same level as the front end of the first conveyor unit.

The scanning device which is actuated by the passage of the front and rear edges of each hide along the first conveyor belt may consist ofa simple photoelectric device ofa conventional type. The scanning operation may, however, also be effected by other suitable means, for example, by a jet of compressed air which is interrupted by the passage of the hide along the first conveyor belt.

Another feature of the invention consists in the provision of a control mechanism which is adapted to control the movements of the second conveyor unit and its belt and essentially consists of pneumatically operated elements including a control element which is controlled by the scanning device and is adapted to carry out a control stroke which may be adapted to he geometric conditions of the particular stacking apparatus with which it is to be associated. When the light beam or the air jet of the scanning device is interrupted by the front edge of the forwardly traveling hide on the first conveyor belt and until the rear edge of the hide passes out of the light beam or air jet, the mentioned control element carries out a control stroke at a certain constant speed. As soon as the rear edge of the hide emerges from the light beam, so that the beam hits upon the photoelectric cell, the latter actuates the control element to carry out the residual part of its stroke, that is, the distance of its total stroke minus that of its control stroke, at twice its former speed and actuates at the end of this residual stroke a control valve which effects the forward movement of the second conveyor unit away from the fixed first conveyor unit.

Since the control mechanism according to the invention is composed of pneumatically actuated elements, it may be built at a relatively low cost. Furthermore, it is of a very simple construction and very reliable in operation. The important concept of this control mechanism relies upon the fact that the control element carries out the first part of its total stroke, i.e. the control stroke, at a certain speed and the remainder of its stroke, i.e. the residual stroke, at twice its former speed. Since the length of the control stroke is directly proportional to the length of the hide and therefore also indicates the position of the center of the hide, the residual stroke will be the shorter the longer the hide. Since this residual stroke is carried out at twice the speed of the control stroke, the control valve which starts the forward movement of the second conveyor unit and thus also the reversal of the direction of travel of its conveyor belt, will be actuated the sooner the shorter the residual stroke will be, that is, the longer the hide willbe. This results from the fact that the center of a long hide reaches a predetermined point above the head of the hide support sooner than the center of a short hide which causes the residual stroke of the control element to be longer and the moment of the actuation of the control valve to occur accordingly at a later time.

The control element is preferably provided in the form of a piston which is slidable in a pneumatic cylinder, the work chamber of which is supplied with compressed air which previously passes through two preadjusted throttle valves which are connected in series with this chamber. One of these throttle valves controls the constant velocity of the air during the control stroke of the piston in this cylinder, while the other throttle valve controls the constant double velocity of the air during the residual stroke of the piston. The first throttle valve is then actuated by the first impulse of the scanning device which is produced by the front edge of the hide traveling along the first conveyor belt, while the second throttle valve is actuated by the second impulse of the scanning device which is produced by the rear edge of the hide.

According to another feature of the invention, a springloaded four-way valve is interposed between thesource of compressed air and these two throttle valves. The control air for operating this four-way valve is supplied from .a control .valve which is actuated by the scanning device in such a manner that, when the light beam of the latter is interrupted by the passage of the hide, this control valve supplies the four way valve with control air whereby this last valve is actuated so as to permit the compressed air to pass through one of the throttle valves and then at a constant velocity to the pneumatic cylinder the piston of which then carries out its control stroke of a length which is in proportion to the length of the hide. When the light beam ofthe scanning device is no longer interrupted by the hide, that is, when the rear edge of thehide emerges from the light beam, the control air for the four-way valve is discharged to the outside and the four-way valve will therefore return underthe action of its return spring to, its original position in which the compressed air may flow through the second throttle valve and then at twice its former velocity to the pneumatic cylinder the piston of which then carries out its residual stroke at twice the speed of its previous control stroke. From the above description it is evident that the invention provides very simple means for actuating the control element which actuates the control valve which effects the forward movement of the second conveyor unit away from the first unit.

In the operation of the stacking apparatus according to the invention and its control mechanism it is important to remember that when the rear edge of a hide on the first conveyor belt passes beyond the scanning device, for example, by leaving its light beam, the center of the hide still has to travel for a certain distance until it reaches the positionvertically above the center of the head ofthe hide support. The scanning device must therefore be spaced from the vertical axis of this head at a distance which is larger than one half of the greatest length of any hide to be stacked. ,The length of the control stroke of the control element, i.e. the piston in the pneumatic .cylindcr, is then proportional to this distance.

A very simple embodiment of the invention may be attained by mounting the control element, for example, the pneumatic cylinder, in a position in which, when its movable part, for example, the piston, is in its original position, it is spaced at a distance corresponding to the length of its control stroke, from an actuating element of the control valve which it is adapted to actuate. This distance is preferably adjustable to permit the control mechanism to be employed for stacking apparatus of different geometric dimensions. The full'stroke of the control element which is independent of the length of the control stroke may, be then .made ofsuch a length thateven under the most unsuitable geometric dimensions, that is, at a very large distance between the scanning device and the vertical axis of the head of the hide support, there will still be a certain clearance to permit the control stroke to be adjusted.

These and further features and advantages of the present invention will become more clearly apparent from the following detailed description thereof which is to be read with reference to the accompanying drawings, in which FIG. 1 shows a diagrammatic side view ofdifferent stages of the operation of a stacking apparatus according to the invention for centrally depositing each hide upon :1 hide support and on each other in a manner so that the same side of all hides of the stack face in the same direction in which they are supplied bythe first conveying belt;

FIG. 2 shows a diagrammatic side view of the stacking apparatus according to FIG. ll, in which the second conveyor belt is operated in such a manner that the hides are deposited on the hide support and on each other by being turned upside down to the position in which they are supplied by the first conveyor belt;

FIG. 3 shows a diagrammatic side viewof the driving means of the first and second conveyor belts and of the means for moving the second conveyor unit and for reversing the direction of travel of the belt of the latter; while FIG. i shows a block diagram of the circuit of the pneumatic control mechanism according to the invention.

In the drawings, FIGS. 1 and 2 illustrate several stages a to d and a to f, respectively, of the operation of the apparatus according ,to the invention. This apparatus comprises an ascending first conveyor belt 1 and, following this belt, a second conveyor belt 2. Above the conveyor belt I. which is preferably transparent or consists of a plurality of individual narrow belts, which are spaced from each other, one or more light sources 3 or compressed-air nozzles are provided, while underneath the upper strand of belt 1 a corresponding number of photoelectric cells 4 or pressure receivers are mounted.

Underneath the belts l and 2 a hide support 5 may be placed which is preferably movable and on which the hides 6 are to be stacked. The conveyor belt l is movable only in one direction and the pulleys thereof are mounted in fixed positions. The front or delivery end of the upper strand of belt 1 is located. above the hide support 5 and is offset at a certain distance to the rear of the latter, that is, toward the left in the drawings. The depositing belt 2 together with its pulleys is, however, movable between a position in accordance with the stages a to b in FIG. 1, in which the rear end of its upper strand is located underneath the delivery end of the conveyor belt 1, and a position according to the stages 0 and din which the rear end of belt 2 is longitudinally spaced from the delivery end of belt ll, that is, in the drawings at the right of its former position and above the hide support 5. When belt 2 is in this forward shifted position, the rear end of its upper strand and the delivery end of belt 1 are spaced at the same distance from the vertical axis of the hide support 5 and are also located at substantially the same level above the head of the hide support.

The skins or hides 6 the center of which is indicated by the letter M are deposited successively upon the upper strand of the conveyor belt 1 and then conveyed by the latter toward the support 5. As soon as the front edge of a hide reaches the light source 3, as shown in stage a in FIG. 1, the light beam will be interrupted whichcauses the control element of a control mechanism to be actuated which will be subsequently described with. reference to FIG. 4-. The rear end of the upper strand of the depositing belt 2 is then located underneath the delivery end of the conveyor belt 1.

The conveyor belt 1 then conveys the hide 6 further at a constant speed until it is taken. up by the second conveyor belt 2, as shown in stage b in FIG. 1. Finally, the hide 6 reaches a position in which its rear edge passes the light source 3. The length of time of the travel of the hide during which the light beam will be interrupted and the distance of the resulting movement of the control element are directly proportional to the length of thehide 6 and thus also determine substantially the location of the center M of the hide. The hide 6 is then to be deposited on the support 5 so that its center M will be located above the narrow head of this support.

The distance between the light source 4 and the central axis of the support 5 should be larger than one half of the length of the longest hide so that the hide must always travel for an additional distance until its center M will be located directly above the head of the support 5. Therefore, the stage b of the operation in which the rear edge of the hide 6 just passes beyond the light beam, the center M of the hide will not as yet be located above the head of the support 5.

The remainder of the distance of travel of hide 6 is proportional to the remainder of the distance of the movement of the control element of the control mechanism. When the center of the hide 6 has reached approximately the vertical axis of the support 5 and is therefore located approximately above the head of the support, the control element has also traveled the predetermined residual distance and then actuates a control valve which starts the movement of the second conveyor unit 2 toward the right and at the same time stops the conveying movement of the conveyor belt of this unit. When the belt 2 has reached the position as shown in stage in FIG. 1, its conveying movement is automatically started in the opposite direction as indicated by the arrow in stages 0 and d in FIG. 1, so that the two belts I and 2 now travel in the directions toward each other with the result that the center M of the hide 6 drops upon the head of the support and its two parts at both sides of the center M rest on the sides of the support.

Belt 2 may thereafter again be moved back to its original position according to stage a, whereupon a new cycle of operations may start. The hides 6 may in this manner be stacked on each other in a position in which the center of each hide is deposited on the center of the next lower hide and vertically above the head of the support 5 and the sides at both sides of this center rest on the front and rear sides of the hide support.

FIG 2 illustrates a modification of the apparatus as shown in FIG. 1 which differs essentially from the latter only by a different manner of its operation. In the stages a and b, the hide 6 travels again along the conveyor belt 1 and thereby interrupts the light beam of the light source 4 and then passes to the depositing belt 2. By scanning the length of the hide by means of the light beam, the position of the center M of the hide is again determined which, in turn, results in a movement of the control element for a certain distance. As indicated in stage c of FIG. 2, the hide is then taken up entirely by the second conveyor belt 2 which by means of a followup control then moves with its pulleys forwardly and away from the conveyor belt 1 to the position as shown in stage d of FIG. 2, in which the direction of travel of belt 2 is reversed so that the hide is conveyed toward the support 5. What is now the front edge of hide 6 then passes over and hangs down from the rear delivery end of belt 2 until the hide reaches a position in which its center M has just passed beyond and hangs down from this delivery end, as shown in stage e of FIG. 2. The point of time when hide 6 reaches this position corresponds to the point of time in which the hide according to FIG. 1 has reached the stage c. The two apparatus according to FIGS. 1 and 2 differ from each other insofar as their operation is concerned in that in stage 0 of FIG. 1 the hide is still held at both sides of its center M by the two belts l and 2, while in stage e of FIG. 2 it is only held at one side on belt 2. The control functions of the two apparatus also differ insofar as, after the length of the hide has been scanned by the light beam of the source 3, the control element of both apparatus have to travel for different distances which are determined by the length of the hide as measured photoelectrically and by the geometric dimensions of the apparatus.

When the apparatus according to FIG. 2 reaches the position of stage e in which the control element has reached the end of its residual travel, it actuates the control valve which causes the second conveyor unit with belt 2 to be moved back to its original position in which its rear end is located in the stage f underneath the delivery end of the conveyor belt 1.

Contrary to the apparatus according to FIG. I, however, the movement of belt 2 is not reversed when it reaches as a unit its original position as shown in stagef. During this movement of belt 2, the hide is deposited centrally in the support 5 and is thereby turned upside down to the position in which it is deposited on the support Sin FIG. 1.

It is evident from the above description that in both apparatus according to FIGS. 1 and 2 the hides 6 may be stacked in a straddling position on the support 5 so that their centers M will be disposed on each other, although according to FIG. 2 the hides will additionally be turned over while being deposited on the support and on each other. By combining the functions of the two apparatus with each other so that the apparatus is alternately operated according to FIG. 1 and then according to FIG. 2, the hides may be stacked on each other on the support 5 so that the flesh sides of each pair of hides of the stack will face each other and will thus remain uniformly moistened. Then will be no dead times nor idling movements during such an operation since, for example, the end position of the second conveyor belt 2 at the completion of one cycle of operations in stage f of FIG. 2 corresponds to the starting position of this belt for the following cycle in stage a of FIG. 1.

FIG. 3 illustrates diagrammatically one preferred embodiment of a drive mechanism for the first conveyor belt I and the second conveyor belt 2. The first conveyor belt 1 is located within a frame 11 and driven by a motor 13 by means of a drivebelt l4 and a drive pulley 12. Frame 11 is provided with a stand 15 for the motor 13 which is followed by a wider plate 16.

The second conveyor belt 2 is located within a separate frame 17 which may be shifted from one to another of two end positions in a guideway on a frame plate 16. For this purpose, the drive pulley 18 of the second conveyor belt is guided within a slot 19 in plate 16. One of these end positions of frame 17, as indicated in dot-and-dash lines in FIG. 3 corresponds to the position of belt 2 in the stages a and b in FIG. 1 or in the stages a to c andfin FIG. 2, while the other end position of frame 17 as shown in FIG. 3 in dotted lines corresponds to the position of belt 2 in the stages 0 and din FIG. 1 or in the stages d and e in FIG. 2. For shifting the second conveyor belt 2 with its frame 17 from one of these positions to the other, any suitable means, for example, a pneumatic or hydraulic cylinder may be provided.

The drive pulley 12 of the conveyor belt 1 and the drive pulley 18 of the depositing belt 2 are connected by a pair of belts 22 and 23. For this purpose, two additional guide pulleys 20 and 21 are mounted on the frame plate 16 in a position so that these pulleys together with the drive pulley 12 of the conveyor belt 1 form a triangular arrangement and are connected to each other by the belt 23. Drive pulley 12 is further directly connected by the belt 22 to the guide pulley 20. When the drive pulley 18 of the depositing belt 2 is in its one end position as shown in full lines in FIG. 3, it is in driving engagement with the outer side of belt 22, and when it is in its other end position as indicated in dotted lines, it is in driving engagement with the inner side of belt 23. Due to its driving engagement with the opposite sides of the two belts 22 and 23, pulley 18 will be driven in one direction when it is in its end position as shown in full lines in which it is driven by the belt 22 and in the opposite direction when it is moved to the other end position as shown in dotted lines in which it is driven by the other belt 23. Of course, instead of employing two separate belts 22 and 23 which are traveling side by side over the pulleys l2 and 20, it is also possible to employ a single belt which travels from the drive pulley 12 over the guide pulley 20 and from the latter either past pulley 18 or in driving engagement with this pulley when it is in its upper position, and then back to the drive pulley 12 and then over the latter and again over the guide pulley 20 and the second guide pulley 21 and from this pulley either past pulley 18 or in engagement with the latter when it is in its lower position, and then back to the drive pulley 12. The movement of the conveyor belt 2 and its two pulleys including the pulley 18 from one end position to the other are effected by the control mechanism and the mentioned control element thereof which will now be described with reference to FIG. 4.

This FIG. 4 illustrates the circuit of a source of current 30 into which a switch 31 and a solenoid valve 32 are inserted. Switch 31 which is normally in its open position is closed when the light beam of the light source 4 as indicated in FIGS. 1 and 2 is interrupted by the passage of a hide 6 along the conveyor belt 1. Switch 31 therefore closes when the front edge of the hide passes into the light beam and it opens as soon as the rear edge of the hide emerges from the light beam.

When switch 31 is closed, the solenoid valve 32 is energized which then supplies compressed air to a four-way valve 34 and a spring-loaded four-way valve 35 which are connected in seties to a source of compressed air 33, for example, a pressure tank 33, to which a spring-loaded two-way valve 36 is also connected which acts as a switch and is operated mechanically by means of a piston 39 which is slidable in a cylinder and forms the control element as previously mentioned. The chamber in this cylinder in front of piston 39 is connected through a throttle 37 to the port b of the four-way valve 34, while the piston itself is acted upon by the compressed air which is supplied from the tank 33 via the four-way valve 34, the spring-loaded four-way valve 45, the throttles 43 and 44 and the pressure-reducing valves 41 and 44.

Switch 31 which is mechanically actuated against spring ac tion by piston 39 supplies by means of the solenoid valve 32 the air for returning the four-way valve 34 to its original position and also the control air for actuating a further four-way valve 40 which is connected to the tank 33 and the outlet parts b and d are connected to the two chambers at both sides of the piston of another cylinder 47 which effects the movements of the second conveyor belt unit 2 from the position near the conveyor belt 1 to the position spaced therefrom and vice versa, as indicated in FIGS. l and 2. The compressed air coming from the outlet part d of the four-way valve 40 may flow also through a throttle 46 into a chamber at one side of a piston in a cylinder 45 which operates as a retarder, and the other chamber of which is connected through a pressure reducer, not shown, to the pressure tank 33 and is thus acted upon by the reduced pressure of this tank. The air which flows out of this chamber of cylinder 45 serves for returning the four-way valve 40 to its original position.

The mode of operation of the control mechanism as above described is as follows:

As soon as the front edge of a hide '6 passes into the light beam of the light source 3 as indicated in FIGS. 1 and 2, switch 31 is closed and remains closed as long as the light beam is interrupted by the hide. As soon as switch 31. is closed, the solenoid of valve 31 is energized so that this valve is moved from its vented position as shown in FIG. 4 to a position in which the inlet port a is connected with the outlet port 12. The compressed air may then flow from the pressure tank 33 through the solenoid valve 32 and act as control air upon the four-way valves 34 and 35 so that the inlet ports a of each of these valves will be connected with its outlet port d. At the same time, the port b of valve 34 is connected with the exhaust port 0, while from the port b of valve 35 the air can not flow off since its point is closed. The compressed air thus passes from the tank 33 through the ports a and d of valve 34 and valve 35, throttle 43 and the reducing valve 42 as actuating air into cylinder 39. The piston of this cylinder 39 therefore starts its control movement as soon as the front edge ofa hide 6 interrupts the light beam from the light source 3.

The throttle 43 and the reducing valve 42 are adjusted so that the compressed air flows at a certain velocity to the 7 cylinder 39. The air which is compressed by the piston in the other chamber of this cylinder passes through the throttle 37 into the valve 34 at b and is discharged therefrom to the outside at c.

The control movement of piston 39 continues as long as the light beam is interrupted by the hide 6. Consequently, the length of the control movement of piston 39 is proportional to the length ofthe hide..The'factor of this proportionality is allltl ways constant since the piston travels the required distance which is dependent upon the passage of the hide through the light beam always at a constant speed which is predetermined by the throttle 43. When the rear edge of the hide passes out of the light beam, switch 31 and valve 32 will be closed. The control air is then exhausted from valve 34 through the channel b-c of the solenoid valve 32. Since valve 34 is not acted upon by spring pressure, it will at first remain in the position as described in which the ports a and d and the ports b and c are connected. The control air is discharged to the outside at the same time and in the same manner from valve 35, but this valve is returned by its spring to its original position as shown in FIG. 4. The compressed air from tank 33 thus flows through the channel a-d of valve 34, the channel a-b of valve 35, the preadjusted throttle 44, and the pressure reducer 41 to the cylinder containing the piston 39 which is thereby shifted for the residual distance of its travel. Since the total length of travel of this piston is adjusted so as to be in proportion to the geometric dimensions of the stacking apparatus, for example, to he distance between the light source 3 and the central axis of the support 5, the residual distance of travel of piston 39 is directly proportional to this distance and also proportional to the length of the hide. Throttle 44 and the pressure reducer 41 are adjusted so that piston 39 will travel this residual distance in twice the speed as that of the control movement of this piston. Valve 36 which acts as a switch, or the control element thereof at its left side is adapted to be actuated by piston 39 at the end of its full stroke. By varying the positions of piston 39 and valve 36 relative to each other it is possible to adapt the control mechanism to the particular geometric conditions of the stacking apparatus with which it is to be associated. Therefore, at the time when the piston arrives at the end of its residual distance of travel, the center M of a hide 6 will be located above the center of the support 5. The longer the hide, the greater will be the distance of the control movement and the shorter the distance of the residual movement. Since the piston travels during this residual movement at twice the speed of the control movement, the point of time when switch 36 will be actuated will be reached very quickly. Therefore, when the rear edge of a longer hide passes beyond the light beam 4, its center M will reach the vertical center of the support 5 according to stage 0 of FIG. 1 morequickly than that of a short hide.

The control valve 36 which is actuated at the end of the residual travel of piston 39 is opened against the pressure of a spring. The compressed air from tank 33 then flows through this valve and acts upon valve 34 to reset the same to its original position as shown in FIG. 4, and it further acts as control air upon the four way valve 40 to shift the same to a posi tion in which its inlet port a is connected with the outlet port d and the port b with the exhaust port 0. Since a throttle 33 is interposed between he valves 36 and 34, valve 34 will be reset to its original position with a certain delay. Valve 40 is, however, acted upon directly. The compressed air at its inlet port a then passes through the outlet port (1 to the cylinder 47 the piston of which effects the movement of the second conveyor unit 2 to the position in which it is spaced from the conveyor belt l. The air which is compressed by this piston is discharged through the channel b-c valve 40 to the outside. The compressed air also passes from the outlet port d of valve 40 through a throttle to the retarder 45 the piston of which moves toward the right against the reduced. pressure acting upon its other side. Throttle 46 and the retarder 45 are designed and adjusted so that the piston of the latter will reach its end position when the hide has been moved off the second conveyor belt 2.

Since valve 34 has been previously returned to its original position as shown in FIG. 4 by the control air coming from the control valve 36, the compressed air passes through the channel ab of valve 34 and throttle 37 into the cylinder 3950 that the piston of the latter is likewise returned to its original position. The air which is compressed by the return. movement of the piston is discharged to the outside. via the reducing valve 41, the throttle 44, the channel b-a of valve 35 and the channel d-e of valve 34.

When the piston of the retarder 45 has reached its end position, the air compressed in front of this piston flows to the valve 40 and thereby moves the latter likewise to the position as shown in FIG. 4. The compressed air therefore fiows through the channel a-b of valve 40 to cylinder 47. The air which is compressed by the piston of this cylinder flows off to the outside through the channel d-e of valve 40 so that the second conveyor unit 2 will be moved back to its position near the conveyor belt 1. The stacking apparatus is thus again in its original position and the control mechanism in its position as shown in FIG. 4.

A feature of the control mechanism according to the invention which is of very great importance consists in the fact that, while the length of a hide is being scanned by the light beam, that is, while the latter is interrupted by the hide, and while the piston 39 moves for a certain distance in proportion with this length, this movement is carried out at a certain speed, whereas the residual part of the movement of this piston is carried out at twice the previous speed. In this manner it is possible by very simple structural means to determine very accurately the point of time at which the center of each hide is located vertically above the center of the support upon which the hides are to be deposited on each other. The present invention further permits for the first time the use of pneumatic control means for stacking apparatus. Finally, the control mechanism according to the invention may be very easily adapted to the particular geometric dimensions of different stacking apparatus since it is for this purpose only necessary to vary the distance between the piston of cylinder 39 and the control valve 36.

Although my invention has been illustrated and described with reference to the preferred embodiment thereof, 1 wish to have it understood that it is in no way limited to the details of such embodiment but is capable of numerous modifications within the scope of the appended claims.

Having thus fully disclosed my invention, what I claim is:

1. An apparatus for stacking hides or the like centrally of their individual length on each other on a support comprising a first and a second conveyor unit longitudinally behind each other and each having a conveyor belt forming a first belt and a second belt, said first unit being mounted in a fixed position, first driving means for moving said first belt continuously at a constant speed in a first direction so as to move a hide on its upper side toward said second unit, scanning means for determining the length of said hide while traveling along said first belt and for also determining the center of the length of said hide while traveling along said first belt and for also determining the center of the length of said hide, a hide support underneath the adjacent ends of said units, the front end of said first unit being located at the rear of and at a certain distance from the central vertical axis of said hide support, means for stopping said second unit for a certain length of time in a first position in which its rear end is located closely adjacent to the front end of said first unit, second driving means for then moving said second belt in the same direction and at the same speed as said first belt until said second belt has received at least a part of the length of said hide from said first belt, means for then shifting said second unit from said first position forwardly to a second position in which the rear end of said second unit is located forwardly of and spaced at the same distance from said vertical axis of said hide support as the front end of said first unit, means for reversing the direction of movement of said second driving means so as to reverse the movement of said second belt when said second unit arrives in said second position so that the upper sides of both belts move at an equal speed toward each other and said hide is deposited centrally on said hide support or on the center of a hide which has been previously deposited, and control means responsive to the actuation of said scanning means for controlling said second driving means and said reversing, shifting and stopping means.

2. An apparatus as defined in claim 1, in which when said second conveyor unit arrives in said second position, the front and rear end portions of said hide are disposed on both belts and the center of said hide is disposed in the gap between said belts and intersects said central vertical axis of said hide support so that by the subsequent travel of the upper sides of said belts at the same speed toward each other, the center of said hide bulges downwardly through said gap and is deposited on the center of the head of said hide support, while said front and rear end portions of said hide are thereafter deposited on the front and rear sides of said support, the upper side of said hide while located on said belts also facing upwardly on said support.

3. An apparatus as defined in claim 1, in which in said first position the rear end of said second conveyor unit is disposed underneath the front end of said first unit, said second belt while traveling in the same direction as said first belt receiving said entire hide from said first belt, said control means being adapted to stop the forward travel of said second belt with said hide thereon while said second unit moves to said second position and then to start the rearward travel of said second belt when said second unit is stopped in said second position so that said hide travels over the rear end of said second unit to a position in which slightly more than one half of the length of said hide including its center is suspended from the rear end of said second unit and the rear end of said hide is located at the rear side of said hide support, and means controlled by said control means for then moving said second unit back to its first position while said second belt continues its rearward travel and thereby deposits the center of said hide on the center of the head of said hide support and then deposits the remainder of said hide upon the front side of said hide supports so that said hide is turned upside down on said hide support relative to its position while located on said belts.

4. An apparatus as defined in claim 2, in which in said first position the rear end of said second conveyor unit is disposed underneath the front end of said first unit and above said hide support, while in said second position the rear end of said second unit is disposed substantially at the same level as the front end of said first unit, said control means being adapted further to control the movements of said second unit and its belt in such a manner that, after said second unit has returned to said first position and said hide has been deposited on said hide support, said control means reverse the direction of travel of said second belt so as to move again in the same direction as said first belt until the next hide traveling along said first belt and past said scanning means has been fully transferred to said second belt, said control means being adapted then to stop the forward travel of said belt with said next hide thereon and to start the movement of said second unit from said first position to said second position and then to start the rearward travel of said second belt while said second unit is stopped in said second position so that said next hide travels over the rear end of said second unit to a position in which slightly more than one half of the length of said next hide including its center is suspended from the rear end of said second unit and the rear end of said next hide is located at the rear side of said hide support and said first hide thereon, and means controlled by said control means for then moving said second unit back to said first position while said second belt continues its rearward travel and thereby deposits the center of said next hide on the center of said first hide on said hide support and then deposits the remainder of said next hide upon the front side of said hide support and said first hide thereon so that said next hide is turned upside down to the position of said fist hide on said hide support.

5. An apparatus as defined in claim 1, in which said driving means comprise a motor, a first drive wheel driven by said motor for driving said first conveyor belt, guide wheel means, said first drive wheel and said guide wheel means being mounted in fixed positions, a second drive wheel for driving said second conveyor belt, and endless driving means would around said first drive wheel and said guide wheel means and driven constantly by said first drive wheel, said shifting and reversing means comprising means for shifting said second drive wheel from a first end position, in which it is applied against one side of said driving means so as to drive said second belt in one direction to a second end position in which said second drive wheel is applied against the other side of said driving means so as to drive said second belt in the opposite direction, said shifting and reversing means also forming said stopping means during the periods in which said second drive wheel is out of engagement with either side of said driving means.

6. An apparatus as defined in claim 5, in which said guide wheel means comprise two guide wheels, said first drive wheel and said two guide wheels being mounted in a substantially triangular arrangement, said second drive Wheel being disposed at the inner side of the triangle, said endless driving means having a first outer stringer extending from said first drive wheel to a first of said two guide wheels, and a second inner stringer extending from said first guide wheel back to and over said first drive wheel, and a third stringer extending also from said first drive wheel over said first and second guide wheels and back to said first drive wheel, said shifting and reversing means being adapted to apply said second drive wheel alternately against the outer side of said second inner stringer or against the inner side of said third stringer.

7. An apparatus as defined in claim 6, in which said first and second stringers form the two stringers of one endless driving element and said third stringer forms a second endless driving element, said two driving elements running laterally adjacent to each other over said first drive wheel and said first guide wheel,

8. An apparatus as defined in claim 5, in which said shifting and reversing means comprise guide means for guiding said second unit from a first position in which said second drive wheel is in its first end position to a second position in which said second drive wheel is in its second end position, the rear end of said second unit when in one of said positions, in which said hide is at least partly received by said second belt from said first belt, being located substantially underneath the front end of said first unit, the rear end of said second unit when in its other position, in which said second unit is moved forwardly away from said first unit, being located at substantially the same level as the front end of said first unit.

9. An apparatus as defined in claim 1, in which said scanning means comprise at least one photoelectric cell at one side of said first belt, and at least one light source at the other side of said first belt for throwing a light beam through said belt upon said cell when said beam is not interrupted by the passage of a hide along said first belt.

10. An apparatus as defined in claim 9, in which said control means comprise a control element responsive to the actuation of said cell occurring at the passage of the front and rear edges of said hide during its travel along said first belt, said control element being adapted to carry out a control stroke having a constant speed in proportion to the constant speed of travel of said first belt and having a length in proportion to the length of said hide as determined by the period between the passage of said front and rear edges of said hide into and out of said light beam, said control element being further adapted to carry out a residual stroke at a certain higher speed than that of said control stroke during the period in which no hide interrupts said light beam and the latter strikes upon said cell, said control means further comprising a control valve adapted to be actuated by said control element at the end of its residual stroke so as to start the forward movement of said second conveyor unit away from said first unit.

llll. An apparatus as defined in claim it), in which said control element consists of a pneumatic cylinder and a piston slidable therein, said control means further comprising a source of compressed air, a conduit connecting said source to said cylinder at one side of said piston, a pair of preadjustable throttle valves inserted into said conduit and connected in parallel, one of said valves bein adapted to control the constant velocity of the compresse air supplied to said cylinder for moving said piston during said control stroke and the other valve being adapted to control the constant higher velocity of said compressed air for moving said piston during said residual stroke.

l2. An apparatus as defined in claim ill, in which said con trol means further comprise a spring-retumed four-way valve interposed between said pair of throttle valves and said compressed-air source, a control valve adapted to be actuated by said scanning means and connected at one side to said source and at the other side to said four-way valve for operating the latter so that the compressed air passes therethrough and through one of said throttle valves to said cylinder for moving said piston at a constant speed to carry out its control stroke when said light beam is interrupted by a hide on said first belt, while when said light beam is not interrupted by a hide, said compressed air for operating said four-way valve in discharged from said control valve to the outside and said four-way valve is then returned by its return spring to its original position in which the compressed air passes through said four-way valve and said second throttle valve to said cylinder so as to move said piston at said higher speed to carry out said residual stroke.

13. An apparatus as defined in claim it), in which said scanning means are spaced from the central vertical axis of said hide support at a distance larger than one half of the greatest length of any hide to be stacked, said control stroke of said control element having a length in proportion to said distance.

M. An apparatus as defined in claim 10, in which when said control element is in its original inactive position, it is spaced from said control valve at a certain distance, said control element and said control valve being adjustable relative to each other for varying said distance. 

1. An apparatus for stacking hides or the like centrally of their individual length on each other oN a support comprising a first and a second conveyor unit longitudinally behind each other and each having a conveyor belt forming a first belt and a second belt, said first unit being mounted in a fixed position, first driving means for moving said first belt continuously at a constant speed in a first direction so as to move a hide on its upper side toward said second unit, scanning means for determining the length of said hide while traveling along said first belt and for also determining the center of the length of said hide while traveling along said first belt and for also determining the center of the length of said hide, a hide support underneath the adjacent ends of said units, the front end of said first unit being located at the rear of and at a certain distance from the central vertical axis of said hide support, means for stopping said second unit for a certain length of time in a first position in which its rear end is located closely adjacent to the front end of said first unit, second driving means for then moving said second belt in the same direction and at the same speed as said first belt until said second belt has received at least a part of the length of said hide from said first belt, means for then shifting said second unit from said first position forwardly to a second position in which the rear end of said second unit is located forwardly of and spaced at the same distance from said vertical axis of said hide support as the front end of said first unit, means for reversing the direction of movement of said second driving means so as to reverse the movement of said second belt when said second unit arrives in said second position so that the upper sides of both belts move at an equal speed toward each other and said hide is deposited centrally on said hide support or on the center of a hide which has been previously deposited, and control means responsive to the actuation of said scanning means for controlling said second driving means and said reversing, shifting and stopping means.
 2. An apparatus as defined in claim 1, in which when said second conveyor unit arrives in said second position, the front and rear end portions of said hide are disposed on both belts and the center of said hide is disposed in the gap between said belts and intersects said central vertical axis of said hide support so that by the subsequent travel of the upper sides of said belts at the same speed toward each other, the center of said hide bulges downwardly through said gap and is deposited on the center of the head of said hide support, while said front and rear end portions of said hide are thereafter deposited on the front and rear sides of said support, the upper side of said hide while located on said belts also facing upwardly on said support.
 3. An apparatus as defined in claim 1, in which in said first position the rear end of said second conveyor unit is disposed underneath the front end of said first unit, said second belt while traveling in the same direction as said first belt receiving said entire hide from said first belt, said control means being adapted to stop the forward travel of said second belt with said hide thereon while said second unit moves to said second position and then to start the rearward travel of said second belt when said second unit is stopped in said second position so that said hide travels over the rear end of said second unit to a position in which slightly more than one half of the length of said hide including its center is suspended from the rear end of said second unit and the rear end of said hide is located at the rear side of said hide support, and means controlled by said control means for then moving said second unit back to its first position while said second belt continues its rearward travel and thereby deposits the center of said hide on the center of the head of said hide support and then deposits the remainder of said hide upon the front side of said hide supports so that said hide is turned upside down on said hide Support relative to its position while located on said belts.
 4. An apparatus as defined in claim 2, in which in said first position the rear end of said second conveyor unit is disposed underneath the front end of said first unit and above said hide support, while in said second position the rear end of said second unit is disposed substantially at the same level as the front end of said first unit, said control means being adapted further to control the movements of said second unit and its belt in such a manner that, after said second unit has returned to said first position and said hide has been deposited on said hide support, said control means reverse the direction of travel of said second belt so as to move again in the same direction as said first belt until the next hide traveling along said first belt and past said scanning means has been fully transferred to said second belt, said control means being adapted then to stop the forward travel of said belt with said next hide thereon and to start the movement of said second unit from said first position to said second position and then to start the rearward travel of said second belt while said second unit is stopped in said second position so that said next hide travels over the rear end of said second unit to a position in which slightly more than one half of the length of said next hide including its center is suspended from the rear end of said second unit and the rear end of said next hide is located at the rear side of said hide support and said first hide thereon, and means controlled by said control means for then moving said second unit back to said first position while said second belt continues its rearward travel and thereby deposits the center of said next hide on the center of said first hide on said hide support and then deposits the remainder of said next hide upon the front side of said hide support and said first hide thereon so that said next hide is turned upside down to the position of said fist hide on said hide support.
 5. An apparatus as defined in claim 1, in which said driving means comprise a motor, a first drive wheel driven by said motor for driving said first conveyor belt, guide wheel means, said first drive wheel and said guide wheel means being mounted in fixed positions, a second drive wheel for driving said second conveyor belt, and endless driving means would around said first drive wheel and said guide wheel means and driven constantly by said first drive wheel, said shifting and reversing means comprising means for shifting said second drive wheel from a first end position, in which it is applied against one side of said driving means so as to drive said second belt in one direction to a second end position in which said second drive wheel is applied against the other side of said driving means so as to drive said second belt in the opposite direction, said shifting and reversing means also forming said stopping means during the periods in which said second drive wheel is out of engagement with either side of said driving means.
 6. An apparatus as defined in claim 5, in which said guide wheel means comprise two guide wheels, said first drive wheel and said two guide wheels being mounted in a substantially triangular arrangement, said second drive wheel being disposed at the inner side of the triangle, said endless driving means having a first outer stringer extending from said first drive wheel to a first of said two guide wheels, and a second inner stringer extending from said first guide wheel back to and over said first drive wheel, and a third stringer extending also from said first drive wheel over said first and second guide wheels and back to said first drive wheel, said shifting and reversing means being adapted to apply said second drive wheel alternately against the outer side of said second inner stringer or against the inner side of said third stringer.
 7. An apparatus as defined in claim 6, in which said first and second stringers form the two stringers oF one endless driving element and said third stringer forms a second endless driving element, said two driving elements running laterally adjacent to each other over said first drive wheel and said first guide wheel.
 8. An apparatus as defined in claim 5, in which said shifting and reversing means comprise guide means for guiding said second unit from a first position in which said second drive wheel is in its first end position to a second position in which said second drive wheel is in its second end position, the rear end of said second unit when in one of said positions, in which said hide is at least partly received by said second belt from said first belt, being located substantially underneath the front end of said first unit, the rear end of said second unit when in its other position, in which said second unit is moved forwardly away from said first unit, being located at substantially the same level as the front end of said first unit.
 9. An apparatus as defined in claim 1, in which said scanning means comprise at least one photoelectric cell at one side of said first belt, and at least one light source at the other side of said first belt for throwing a light beam through said belt upon said cell when said beam is not interrupted by the passage of a hide along said first belt.
 10. An apparatus as defined in claim 9, in which said control means comprise a control element responsive to the actuation of said cell occurring at the passage of the front and rear edges of said hide during its travel along said first belt, said control element being adapted to carry out a control stroke having a constant speed in proportion to the constant speed of travel of said first belt and having a length in proportion to the length of said hide as determined by the period between the passage of said front and rear edges of said hide into and out of said light beam, said control element being further adapted to carry out a residual stroke at a certain higher speed than that of said control stroke during the period in which no hide interrupts said light beam and the latter strikes upon said cell, said control means further comprising a control valve adapted to be actuated by said control element at the end of its residual stroke so as to start the forward movement of said second conveyor unit away from said first unit.
 11. An apparatus as defined in claim 10, in which said control element consists of a pneumatic cylinder and a piston slidable therein, said control means further comprising a source of compressed air, a conduit connecting said source to said cylinder at one side of said piston, a pair of preadjustable throttle valves inserted into said conduit and connected in parallel, one of said valves being adapted to control the constant velocity of the compressed air supplied to said cylinder for moving said piston during said control stroke and the other valve being adapted to control the constant higher velocity of said compressed air for moving said piston during said residual stroke.
 12. An apparatus as defined in claim 11, in which said control means further comprise a spring-returned four-way valve interposed between said pair of throttle valves and said compressed-air source, a control valve adapted to be actuated by said scanning means and connected at one side to said source and at the other side to said four-way valve for operating the latter so that the compressed air passes therethrough and through one of said throttle valves to said cylinder for moving said piston at a constant speed to carry out its control stroke when said light beam is interrupted by a hide on said first belt, while when said light beam is not interrupted by a hide, said compressed air for operating said four-way valve in discharged from said control valve to the outside and said four-way valve is then returned by its return spring to its original position in which the compressed air passes through said four-way valve and said second throttle valve to said cylinder so as to move said piston at said higher speed to carry out said residual stroke.
 13. An apparatus as defined in claim 10, in which said scanning means are spaced from the central vertical axis of said hide support at a distance larger than one half of the greatest length of any hide to be stacked, said control stroke of said control element having a length in proportion to said distance.
 14. An apparatus as defined in claim 10, in which when said control element is in its original inactive position, it is spaced from said control valve at a certain distance, said control element and said control valve being adjustable relative to each other for varying said distance. 